[PATCH 0/2] Remove Xen PVH dependency on PCI

[PATCH 0/2] Remove Xen PVH dependency on PCI

[Jason Andryuk]

A Xen PVH domain doesn't have a PCI bus or devices, so it doesn't need
PCI support built in.  Currently, XEN_PVH depends on XEN_PVHVM which
depends on PCI.

The first patch introduces XEN_PVHVM_GUEST as a toplevel item and
changes XEN_PVHVM to a hidden variable.  This allows XEN_PVH to depend
on XEN_PVHVM without PCI while XEN_PVHVM_GUEST depends on PCI.

The second patch moves XEN_512GB to clean up the option nesting.

Jason Andryuk (2):
  xen: Remove Xen PVH/PVHVM dependency on PCI
  xen: Kconfig: nest Xen guest options

 arch/x86/xen/Kconfig | 38 ++++++++++++++++++++++----------------
 drivers/xen/Makefile |  2 +-
 2 files changed, 23 insertions(+), 17 deletions(-)

-- 
2.26.2

[PATCH 1/2] xen: Remove Xen PVH/PVHVM dependency on PCI

[Jason Andryuk]

A Xen PVH domain doesn't have a PCI bus or devices, so it doesn't need
PCI support built in.  Currently, XEN_PVH depends on XEN_PVHVM which
depends on PCI.

Introduce XEN_PVHVM_GUEST as a toplevel item and change XEN_PVHVM to a
hidden variable.  This allows XEN_PVH to depend on XEN_PVHVM without PCI
while XEN_PVHVM_GUEST depends on PCI.

In drivers/xen, compile platform-pci depending on XEN_PVHVM_GUEST since
that pulls in the PCI dependency for linking.

Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
---
---
 arch/x86/xen/Kconfig | 18 ++++++++++++------
 drivers/xen/Makefile |  2 +-
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
index 218acbd5c7a0..b75007eb4ec4 100644
--- a/arch/x86/xen/Kconfig
+++ b/arch/x86/xen/Kconfig
@@ -39,16 +39,20 @@ config XEN_DOM0
 	  Support running as a Xen PV Dom0 guest.
 
 config XEN_PVHVM
-	bool "Xen PVHVM guest support"
-	default y
-	depends on XEN && PCI && X86_LOCAL_APIC
-	help
-	  Support running as a Xen PVHVM guest.
+	def_bool y
+	depends on XEN && X86_LOCAL_APIC
 
 config XEN_PVHVM_SMP
 	def_bool y
 	depends on XEN_PVHVM && SMP
 
+config XEN_PVHVM_GUEST
+	bool "Xen PVHVM guest support"
+	default y
+	depends on XEN_PVHVM && PCI
+	help
+	  Support running as a Xen PVHVM guest.
+
 config XEN_512GB
 	bool "Limit Xen pv-domain memory to 512GB"
 	depends on XEN_PV
@@ -76,7 +80,9 @@ config XEN_DEBUG_FS
 	  Enabling this option may incur a significant performance overhead.
 
 config XEN_PVH
-	bool "Support for running as a Xen PVH guest"
+	bool "Xen PVH guest support"
 	depends on XEN && XEN_PVHVM && ACPI
 	select PVH
 	def_bool n
+	help
+	  Support for running as a Xen PVH guest.
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index babdca808861..c3621b9f4012 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -21,7 +21,7 @@ obj-$(CONFIG_XEN_GNTDEV)		+= xen-gntdev.o
 obj-$(CONFIG_XEN_GRANT_DEV_ALLOC)	+= xen-gntalloc.o
 obj-$(CONFIG_XENFS)			+= xenfs/
 obj-$(CONFIG_XEN_SYS_HYPERVISOR)	+= sys-hypervisor.o
-obj-$(CONFIG_XEN_PVHVM)			+= platform-pci.o
+obj-$(CONFIG_XEN_PVHVM_GUEST)		+= platform-pci.o
 obj-$(CONFIG_SWIOTLB_XEN)		+= swiotlb-xen.o
 obj-$(CONFIG_XEN_MCE_LOG)		+= mcelog.o
 obj-$(CONFIG_XEN_PCIDEV_BACKEND)	+= xen-pciback/
-- 
2.26.2

Re: [PATCH 1/2] xen: Remove Xen PVH/PVHVM dependency on PCI

[Jan Beulich]

On 14.10.2020 19:53, Jason Andryuk wrote:
> @@ -76,7 +80,9 @@ config XEN_DEBUG_FS
>  	  Enabling this option may incur a significant performance overhead.
>  
>  config XEN_PVH
> -	bool "Support for running as a Xen PVH guest"
> +	bool "Xen PVH guest support"

Tangential question: Is "guest" here still appropriate, i.e.
isn't this option also controlling whether the kernel can be
used in a PVH Dom0?

>  	def_bool n

And is this default still appropriate?

Jan

Re: [PATCH 1/2] xen: Remove Xen PVH/PVHVM dependency on PCI

[Jason Andryuk]

On Thu, Oct 15, 2020 at 4:10 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 14.10.2020 19:53, Jason Andryuk wrote:
> > @@ -76,7 +80,9 @@ config XEN_DEBUG_FS
> >         Enabling this option may incur a significant performance overhead.
> >
> >  config XEN_PVH
> > -     bool "Support for running as a Xen PVH guest"
> > +     bool "Xen PVH guest support"
>
> Tangential question: Is "guest" here still appropriate, i.e.
> isn't this option also controlling whether the kernel can be
> used in a PVH Dom0?

Would you like something more generic like "Xen PVH support" and
"Support for running in Xen PVH mode"?

> >       def_bool n
>
> And is this default still appropriate?

We probably want to flip it on, yes.  PVH is the future, isn't it?

Regards,
Jason

Re: [PATCH 1/2] xen: Remove Xen PVH/PVHVM dependency on PCI

[Jan Beulich]

On 15.10.2020 16:59, Jason Andryuk wrote:
> On Thu, Oct 15, 2020 at 4:10 AM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 14.10.2020 19:53, Jason Andryuk wrote:
>>> @@ -76,7 +80,9 @@ config XEN_DEBUG_FS
>>>         Enabling this option may incur a significant performance overhead.
>>>
>>>  config XEN_PVH
>>> -     bool "Support for running as a Xen PVH guest"
>>> +     bool "Xen PVH guest support"
>>
>> Tangential question: Is "guest" here still appropriate, i.e.
>> isn't this option also controlling whether the kernel can be
>> used in a PVH Dom0?
> 
> Would you like something more generic like "Xen PVH support" and
> "Support for running in Xen PVH mode"?

Yeah, just dropping "guest" would be fine with me. No idea how
to reflect that PVH Dom0 isn't supported, yet.

Jan

Re: [PATCH 1/2] xen: Remove Xen PVH/PVHVM dependency on PCI

[Roger Pau Monné]

On Thu, Oct 15, 2020 at 05:02:21PM +0200, Jan Beulich wrote:
> On 15.10.2020 16:59, Jason Andryuk wrote:
> > On Thu, Oct 15, 2020 at 4:10 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>
> >> On 14.10.2020 19:53, Jason Andryuk wrote:
> >>> @@ -76,7 +80,9 @@ config XEN_DEBUG_FS
> >>>         Enabling this option may incur a significant performance overhead.
> >>>
> >>>  config XEN_PVH
> >>> -     bool "Support for running as a Xen PVH guest"
> >>> +     bool "Xen PVH guest support"
> >>
> >> Tangential question: Is "guest" here still appropriate, i.e.
> >> isn't this option also controlling whether the kernel can be
> >> used in a PVH Dom0?
> > 
> > Would you like something more generic like "Xen PVH support" and
> > "Support for running in Xen PVH mode"?
> 
> Yeah, just dropping "guest" would be fine with me. No idea how
> to reflect that PVH Dom0 isn't supported, yet.

The fact that it isn't supported by Xen shouldn't be reflected on the
Linux configuration, as it's independent. Ie: you could run this Linux
kernel on a future version of Xen where PVH dom0 is supported.

There's already a warning printed by Xen when booting PVH dom0 about
not being a supported mode.

Thanks, Roger.

[PATCH 2/2] xen: Kconfig: nest Xen guest options

[Jason Andryuk]

Moving XEN_512GB allows it to nest under XEN_PV.  That also allows
XEN_PVH to nest under XEN as a sibling to XEN_PV and XEN_PVHVM giving:

[*]   Xen guest support
[*]     Xen PV guest support
[*]       Limit Xen pv-domain memory to 512GB
[*]       Xen PV Dom0 support
[*]     Xen PVHVM guest support
[*]     Xen PVH guest support

Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
---
 arch/x86/xen/Kconfig | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
index b75007eb4ec4..2b105888927c 100644
--- a/arch/x86/xen/Kconfig
+++ b/arch/x86/xen/Kconfig
@@ -26,6 +26,19 @@ config XEN_PV
 	help
 	  Support running as a Xen PV guest.
 
+config XEN_512GB
+	bool "Limit Xen pv-domain memory to 512GB"
+	depends on XEN_PV && X86_64
+	default y
+	help
+	  Limit paravirtualized user domains to 512GB of RAM.
+
+	  The Xen tools and crash dump analysis tools might not support
+	  pv-domains with more than 512 GB of RAM. This option controls the
+	  default setting of the kernel to use only up to 512 GB or more.
+	  It is always possible to change the default via specifying the
+	  boot parameter "xen_512gb_limit".
+
 config XEN_PV_SMP
 	def_bool y
 	depends on XEN_PV && SMP
@@ -53,19 +66,6 @@ config XEN_PVHVM_GUEST
 	help
 	  Support running as a Xen PVHVM guest.
 
-config XEN_512GB
-	bool "Limit Xen pv-domain memory to 512GB"
-	depends on XEN_PV
-	default y
-	help
-	  Limit paravirtualized user domains to 512GB of RAM.
-
-	  The Xen tools and crash dump analysis tools might not support
-	  pv-domains with more than 512 GB of RAM. This option controls the
-	  default setting of the kernel to use only up to 512 GB or more.
-	  It is always possible to change the default via specifying the
-	  boot parameter "xen_512gb_limit".
-
 config XEN_SAVE_RESTORE
 	bool
 	depends on XEN
-- 
2.26.2

Re: [PATCH 2/2] xen: Kconfig: nest Xen guest options

[Jürgen Groß]

On 14.10.20 19:53, Jason Andryuk wrote:
> Moving XEN_512GB allows it to nest under XEN_PV.  That also allows
> XEN_PVH to nest under XEN as a sibling to XEN_PV and XEN_PVHVM giving:
> 
> [*]   Xen guest support
> [*]     Xen PV guest support
> [*]       Limit Xen pv-domain memory to 512GB
> [*]       Xen PV Dom0 support

This has currently a wrong text/semantics:

It should be split to CONFIG_XEN_DOM0 and CONFIG_XEN_PV_DOM0.

Otherwise the backends won't be enabled per default for a PVH-only
config meant to be Dom0-capable.

You don't have to do that in your patches if you don't want to, but
I wanted to mention it with you touching this area of Kconfig.

> [*]     Xen PVHVM guest support
> [*]     Xen PVH guest support
> 
> Signed-off-by: Jason Andryuk <jandryuk@gmail.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen

Re: [PATCH 2/2] xen: Kconfig: nest Xen guest options

[Jason Andryuk]

On Thu, Oct 15, 2020 at 5:42 AM Jürgen Groß <jgross@suse.com> wrote:
>
> On 14.10.20 19:53, Jason Andryuk wrote:
> > Moving XEN_512GB allows it to nest under XEN_PV.  That also allows
> > XEN_PVH to nest under XEN as a sibling to XEN_PV and XEN_PVHVM giving:
> >
> > [*]   Xen guest support
> > [*]     Xen PV guest support
> > [*]       Limit Xen pv-domain memory to 512GB
> > [*]       Xen PV Dom0 support
>
> This has currently a wrong text/semantics:
>
> It should be split to CONFIG_XEN_DOM0 and CONFIG_XEN_PV_DOM0.
>
> Otherwise the backends won't be enabled per default for a PVH-only
> config meant to be Dom0-capable.
>
> You don't have to do that in your patches if you don't want to, but
> I wanted to mention it with you touching this area of Kconfig.

Yes, good point.  I had not considered that.

> > [*]     Xen PVHVM guest support
> > [*]     Xen PVH guest support
> >
> > Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
>
> Reviewed-by: Juergen Gross <jgross@suse.com>

Thanks,
Jason

Re: [PATCH 2/2] xen: Kconfig: nest Xen guest options

[boris.ostrovsky]

On 10/14/20 1:53 PM, Jason Andryuk wrote:
> +config XEN_512GB
> +	bool "Limit Xen pv-domain memory to 512GB"
> +	depends on XEN_PV && X86_64


Why is X86_64 needed here?


-boris

Re: [PATCH 2/2] xen: Kconfig: nest Xen guest options

[Andrew Cooper]

On 15/10/2020 13:37, boris.ostrovsky@oracle.com wrote:
> On 10/14/20 1:53 PM, Jason Andryuk wrote:
>> +config XEN_512GB
>> +	bool "Limit Xen pv-domain memory to 512GB"
>> +	depends on XEN_PV && X86_64
>
> Why is X86_64 needed here?

>512G support was implemented using a direct-mapped P2M, and is rather
beyond the virtual address capabilities of 32bit.

~Andrew

Re: [PATCH 2/2] xen: Kconfig: nest Xen guest options

[boris.ostrovsky]

On 10/15/20 9:10 AM, Andrew Cooper wrote:
> On 15/10/2020 13:37, boris.ostrovsky@oracle.com wrote:
>> On 10/14/20 1:53 PM, Jason Andryuk wrote:
>>> +config XEN_512GB
>>> +	bool "Limit Xen pv-domain memory to 512GB"
>>> +	depends on XEN_PV && X86_64
>> Why is X86_64 needed here?
>> 512G support was implemented using a direct-mapped P2M, and is rather
> beyond the virtual address capabilities of 32bit.
>

Yes, my point was that XEN_PV already depends on X86_64.


-boris

Re: [PATCH 2/2] xen: Kconfig: nest Xen guest options

[Jason Andryuk]

On Thu, Oct 15, 2020 at 9:17 AM <boris.ostrovsky@oracle.com> wrote:
>
>
> On 10/15/20 9:10 AM, Andrew Cooper wrote:
> > On 15/10/2020 13:37, boris.ostrovsky@oracle.com wrote:
> >> On 10/14/20 1:53 PM, Jason Andryuk wrote:
> >>> +config XEN_512GB
> >>> +   bool "Limit Xen pv-domain memory to 512GB"
> >>> +   depends on XEN_PV && X86_64
> >> Why is X86_64 needed here?
> >> 512G support was implemented using a direct-mapped P2M, and is rather
> > beyond the virtual address capabilities of 32bit.
> >
>
> Yes, my point was that XEN_PV already depends on X86_64.

Oh, thanks for catching this.  I re-introduced it by accident when
rebasing the patches.

Regards,
Jason

Re: [SUSPECTED SPAM][PATCH 0/2] Remove Xen PVH dependency on PCI

[Andrew Cooper]

On 14/10/2020 18:53, Jason Andryuk wrote:
> A Xen PVH domain doesn't have a PCI bus or devices,

[*] Yet.

> so it doesn't need PCI support built in.

Untangling the dependences is a good thing, but eventually we plan to
put an optional PCI bus back in, e.g. for SRIOV usecases.

~Andrew

Re: [SUSPECTED SPAM][PATCH 0/2] Remove Xen PVH dependency on PCI

[Jason Andryuk]

On Wed, Oct 14, 2020 at 2:04 PM Andrew Cooper <andrew.cooper3@citrix.com> wrote:
>
> On 14/10/2020 18:53, Jason Andryuk wrote:
> > A Xen PVH domain doesn't have a PCI bus or devices,
>
> [*] Yet.

:)

> > so it doesn't need PCI support built in.
>
> Untangling the dependences is a good thing, but eventually we plan to
> put an optional PCI bus back in, e.g. for SRIOV usecases.

Yes, and to be clear this change doesn't preclude including the PCI
code.  I was just looking to remove code from my VMs that aren't using
PCI devices.

Regards,
Jason

Re: [PATCH 0/2] Remove Xen PVH dependency on PCI

[Jürgen Groß]

[-- Attachment #1.1.1: Type: text/plain, Size: 840 bytes --]

On 14.10.20 19:53, Jason Andryuk wrote:
> A Xen PVH domain doesn't have a PCI bus or devices, so it doesn't need
> PCI support built in.  Currently, XEN_PVH depends on XEN_PVHVM which
> depends on PCI.
> 
> The first patch introduces XEN_PVHVM_GUEST as a toplevel item and
> changes XEN_PVHVM to a hidden variable.  This allows XEN_PVH to depend
> on XEN_PVHVM without PCI while XEN_PVHVM_GUEST depends on PCI.
> 
> The second patch moves XEN_512GB to clean up the option nesting.
> 
> Jason Andryuk (2):
>    xen: Remove Xen PVH/PVHVM dependency on PCI
>    xen: Kconfig: nest Xen guest options
> 
>   arch/x86/xen/Kconfig | 38 ++++++++++++++++++++++----------------
>   drivers/xen/Makefile |  2 +-
>   2 files changed, 23 insertions(+), 17 deletions(-)
> 

Series applied to: xen/tip.git for-linus-5.11


Juergen

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